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                                             155
    SECTION 3.8                                                   Common Data Structures



    associating the names F5, F6, F7, and F8 with objects 6, 8, 10, and 12, respectively.
    Likewise, the XObject subdictionary associates the names Im1 and Im2 with
    objects 13 and 15, respectively.

    Example 3.16

       << /ProcSet [ /PDF /ImageB ]
          /Font << /F5 6 0 R
                     /F6 8 0 R
                     /F7 10 0 R
                     /F8 12 0 R
                >>
          /XObject << /Im1 13 0 R
                        /Im2 15 0 R
                    >>
       >>


3.8 Common Data Structures

    As mentioned at the beginning of this chapter, there are some general-purpose
    data structures that are built from the basic object types described in Section 3.2,
    “Objects,” and are used in many places throughout PDF. This section describes
    data structures for text strings, dates, rectangles, name trees, and number trees.
    The subsequent two sections describe more complex data structures for functions
    and file specifications.

    All of these data structures are meaningful only as part of the document hier-
    archy; they cannot appear within content streams. In particular, the special
    conventions for interpreting the values of string objects apply only to strings
    outside content streams. An entirely different convention is used within content
    streams for using strings to select sequences of glyphs to be painted on the page
    (see Chapter 5). Table 3.31 summarizes the basic and higher-level data types that
    are used throughout this book to describe the values of dictionary entries and
    other PDF data values.

                                 TABLE 3.31 PDF data types
    TYPE                      DESCRIPTION                               SECTION     PAGE

    ASCII string              Bytes containing ASCII characters         3.8.1       157

    array                     Array object                              3.2.5       58

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